The United Kingdom, Ireland, Italy, Germany and France have vaccinated less than 10 percent of their populations, compared with 20 percent in Europe in a typical flu season. As a result, a fraction of the European Union’s 500 million people will be protected against the pandemic virus by early next year.

Public concerns that the vaccines may cause serious side effects have kept some Europeans on the sidelines since governments began vaccinating residents for free in October. That means Europe may donate more doses to poorer countries or experience a surge in hospital admissions if the virus mutates.

“If it’s not in the news anymore and if people don’t experience a lot of severe cases, to them it’s just a flu and not a pandemic flu in a way,” said Christian Ruef, professor of infectious disease and director of infection control at University Hospital Zurich. “The term pandemic to them is probably associated with more serious disease.”

The number of deaths is lower than what was predicted in worst-case scenarios after the virus first struck, Ruef told Bloomberg. Perceptions that the virus is mild may be hampering vaccination, he said.

The European Society of Clinical Microbiology and Infectious Diseases said on Nov. 23 that it was concerned about “mixed levels of uptake” and opposition from anti-vaccine activists challenging the safety of and need for the shot.

“No one should reject a safe and effective vaccine when we are dealing with an unpredictable virus capable of killing children and young adults in their prime,” said Javier Garau, president of the European Society of Clinical Microbiology and Infectious Diseases, based in Basel, Switzerland.

Officials expect the virus to be prevalent again in 2010. The World Health Organization in September decided to include swine flu in the vaccine for seasonal influenza in the next Southern Hemisphere flu season, meaning the agency thinks it’s the most likely H1N1 strain to be circulating.

One bright spot in Europe’s pandemic immunization effort is Scandinavia. A third of Sweden’s 9.2 million people are estimated to have gotten the swine flu shot as of Nov. 20, according to the Swedish Association of Local Authorities and Regions. About 3.3 million doses of vaccine had been delivered to Sweden as of Nov. 20 and demand has outpaced supply.

“Everybody in my family got the shot,” said Jenny Mattisson, 36, a mother of three who lives in a suburb of Stockholm and usually doesn’t get a seasonal flu shot. “Our daughter is in a risk group so we wanted to try to minimize the chance of her getting sick, but I would have taken it anyway. I think it’s a good idea to get the vaccine; it helps slow it from spreading.”

Norway, where mutations in the H1N1 virus have been detected among two patients who died of the flu and one who was severely ill, had vaccinated all 1.2 million people in its risk groups as of Nov. 24, almost 25 percent of its total population, said Bjoerne-Inge Larsen, director general of Norway’s Directorate of Health. Finland has immunized about 1 million people, or 19 percent of its population, the government said on Nov. 26.